Saturday, September 28, 2013

It’s long been known that many organisms are
parasites, i.e., they survive by living off a host. In recent years we’ve
learned that some of them can improve on their life strategy by manipulating
their host’s behavior. A fungus, Ophiocordyceps
unilateralis, will invade an ant’s brain and direct its host to go to the
right height above ground, lock itself into position … and die (Ophiocordycepsunilateralis, 2013). A tapeworm, Schistocephalus
solidus, will infect a fish and cause its host to turn white and prefer the
water surface, thereby making it an easy prey for a passing bird—the next stage
in the worm’s life cycle (Fish diseases and parasites, 2013). A protozoan, Toxoplasma gondii, after being excreted
in cat feces and then picked up by a mouse, will infiltrate the brain of its
new host and neutralize the fear response to the smell of cat urine. The host thus
becomes a way to get back into a cat’s gut—the only place where this protozoan
can sexually reproduce (Ingram et al., 2013).

Ants, fish, mice … The sequence is troubling. What
about us? Have some microbes evolved to manipulate our brains? Perhaps, but it
would be hard to prove. For one thing, we’re continually being infected by seemingly
benign microbes that trigger no symptoms of infection, i.e., fever, pus
formation, immune response, etc. They go about their business without our
knowing they’re inside us.

For another thing, a microbe can permanently alter
our mental wiring and then be removed from our body. The culprit vanishes from
the scene of the crime and leaves only a few ambiguous clues. This is the
conclusion of a recent study on Toxoplasma
gondii. When mice were infected with a weakened strain of this protozoan,
they were able to overcome the infection and clear all traces of it from their
brains. Yet the behavioral change remained:

[…] our data indicate that
infection with all three major North American T. gondii clonal lineages results in loss of innate, hard-wired
aversion to feline predator urine in mice. […] permanent interruption of mouse
innate aversion to feline urine is a general trait of T. gondii infection that occurs within the first three weeks,
independent of parasite persistence and ongoing brain inflammation. (Ingram etal., 2013)

It seems that T.
gondii moves around the host’s brain and alters many neurons without
actually taking up residence in them, apparently by injecting specific proteins
through the cell wall.

Although we’re not a natural host, T. gondii does appear to alter human
behavior:

Toxoplasma-infected
subjects differ from uninfected controls in the personality profile estimated
with two versions of Cattell’s 16PF, Cloninger’s TCI and Big Five
questionnaires. Most of these differences increase with the length of time
since the onset of infection, suggesting that Toxoplasma influences human personality rather than human
personality influencing the probability of infection. Toxoplasmosis increases
the reaction time of infected subjects, which can explain the increased
probability of traffic accidents in infected subjects reported in three
retrospective and one very large prospective case-control study. […] Toxoplasma-infected male students are
about 3 cm taller than Toxoplasma-free
subjects and their faces are rated by women as more masculine and dominant.
These differences may be caused by an increased concentration of testosterone. Toxoplasma also appears to be involved
in the initiation of more severe forms of schizophrenia. At least 40 studies
confirmed an increased prevalence of toxoplasmosis among schizophrenic
patients. Toxoplasma-infected
schizophrenic patients differ from Toxoplasma-free
schizophrenic patients by brain anatomy and by a higher intensity of the
positive symptoms of the disease. (Flegr, 2013)

T. gondii is
being studied for possible behavioral effects mainly because it has attracted
so much attention. But we’re probably being manipulated by other parasites. “A
large number of parasitic organisms probably exist in helminths, protozoa,
fungi, bacteria, archea and viruses that may influence the phenotype of their
human host even more than the Toxoplasma.
These organisms are, however, still waiting for research teams to engage in a
systematic study of their influence on the human host” (Flegr, 2013).

Sunday, September 22, 2013

St. Adalbert freeing Slavic slaves (source). With
the Christianization of Eastern Europe, the trade in fair-skinned women and
boys came to an end.

The white slave trade played a key role in ending
the Dark Ages—this seemingly unending downward spiral that followed the
collapse of the Roman Empire. By the 8th century, the elites of Western Europe
had run out of gold and possessed very little else that could be traded for
luxury Oriental goods. It was at that point in time that the possibility arose
of selling fellow Europeans into slavery, particularly Slavs from the lands
between the Elbe and the Volga.

Yet this historical episode is relatively unknown.
One reason was its semi-illegality. Involuntary servitude wasn’t unlawful in
itself. In fact, most Europeans were bound by long-term ties of submission,
like the serfs who farmed the land. This was an accepted part of life.
Enslavement was even seen as a humane way of dealing with criminals, prisoners
of war, and other people who would otherwise be killed. But this particular form of enslavement meant more
than just inferior status. Some of its aspects contravened both secular law and
Christian morality, notably castration, the breaking up of families, and the
abandonment of individuals who were too old or too young. There was also the
exporting of fellow Europeans to the Muslim world and the prohibition against
letting them learn about the Christian faith. It was for this reason that the
existing term for involuntary servitude—servus—was
felt to be inappropriate. The ethnonym ‘Slav’ thus came to mean a particularly
degraded kind of servant—a slave.

This leads to another reason why this trade is
little talked about. It sheds an unflattering light on our early history. The
end of the Dark Ages was bought at a high moral price, even by medieval
standards. After selling off the family heirlooms, our ancestors began to sell
eunuchs, concubines, and toy boys—all this to get gold and precious fabrics to
adorn their palaces … and churches.

This same price would also make possible the rise of
states in Eastern Europe. When we read that early Polish and Russian kings had
hundreds of wives or concubines, we smile and assume that this sort of thing
was normal in those days. Yet it wasn’t. The slave trade initiated a cultural
revolution that radically transformed social relations throughout pre-Christian
Slavic Europe. Chieftains were previously elected and ruled over small
territories through consensus; now, with Arab gold and silver, some of them had
the means to assert their power unilaterally over much larger territories. A
primitive form of democracy gave way to despotic rule.

Finally, this historical episode sheds an
unflattering light on a group of Jews based in Spain and France who came to be
called Radhanites. Being neither Christian nor Muslim, they were ideal middlemen
for the overland trade route to Muslim Spain. At the other end of this route,
there arose between the 8th and 12th centuries a network of trading posts
across the Slavic lands that stretched from the Elbe in the West to the Volga
in the East.

These trading posts may have eventually given rise
to the Ashkenazi community of Eastern Europe. Admittedly, the usual explanation
is that Jews emigrated to Poland in the wake of
12th-century persecutions in Western Europe. Yet there are earlier references to the presence of Jewish traders in what is now eastern and central Europe:

The appearance of Jews in central
and eastern Europe occurred, it seems, only in the eighth century. It was
linked to two important facts, the first of which was the establishment of a
Jewish cultural and political center in Khazaria, a great Turkish empire whose
center was on the lower Volga. […] The second fact that favored the formation
of Jewish colonies in central and eastern Europe (located east of the Elbe) was
the role played by Jewish merchants in the trade between Western Europe and the
Muslim East.

[…] The Jews of Bohemia are cited
for the first time in the 10th century; the Jews of Prague, in particular, are
mentioned in the biographies of St. Adalbert. The existence of Jewish colonies
in Poland go back only to the early 11th century.

[…] Jewish trade with central and
eastern Europe was from the beginning closely linked to the fact that the
Western Jews, especially the Spanish, French, and Rhineland Jews, played a
major role in the international trade of Western Europe with the Muslim East.
This trade began in the late 8th century at the initiative of Arab and Muslim
traders. Many colonies of Jewish merchants formed along the trading routes that
linked Western Europe to the countries of the Abbasid Caliphate.

[…] We have already mentioned the
existence of Jewish traders in Prague in the late 10th century. The biographies
of St. Adalbert tell us that they trafficked in slaves. There was also in the
early 11th century, we will discuss further, a Jewish establishment at
Przemysl, a town at the crossroads of two trading routes: Prague-Krakow-Kiev
and Hungary-Kiev. The importance of this center is confirmed by the discovery,
made in the mid 19th century of a great treasure of dirhams (Arab silver money)
from the Iranian dynasty of the Samanids, dating from the first half of the
10th century (Lewicki, 1960)

This settlement model is also consistent with the
genetic evidence that Ashkenazi Jews descend from a small founder group of only
300 to 400 individuals who lived about 800 years ago (Carmi et al., 2013).

We should keep in mind that that these merchants
were only a small group within a much larger Jewish community. Moreover, this
trade was shared with at least two other groups: the Vikings, who dominated the
trading routes via the Baltic and the Dnieper, the Don, and the Volga, and the
Khazars, who controlled the Volga trading route. Indeed, the sudden eruption of
Viking raids into Western and Eastern Europe at this time was, to a large
degree, motivated by a desire to cash in on the white slave trade. Captives
from both western and eastern Europe were taken to the trading center at Hedeby
(in present-day Denmark) for sale to Muslim traders (Skirda, 2010, pp. 143-146).

The world was a very different place in the 8th century
and should not be seen through the lens of more recent times. Back then,
Western Europe was a ruined civilization with memories of former grandeur. The
white slave trade offered the ruling classes a way out, either indirectly
through taxation or through direct sale of prisoners of war from the Elbe
frontier. Had Jewish merchants not been available as go-betweens, there would
have been other middlemen. The Vikings and the Khazars, for instance, who
dominated this trade at the eastern and northern ends, would have eventually developed
the overland route through Germany and France to Muslim Spain.

Saturday, September 14, 2013

Can Europeans, and European women in particular,
become objects of trade? The idea seems laughable, since the term ‘slave trade’
almost always brings Africans to mind. Yet there was a time not so long ago
when Europe exported slaves on a large scale. Between 1500 and 1650, Eastern
Europe exported 1.5 million slaves to North Africa, the Middle East, and South
Asia (Fisher, 1972; Kolodziejczyk, 2006). Western Europe exported a little over
a million between 1530 and 1780 (Davis, 2004).

These slaves were taken during hit-and-run raids by
either Crimean Tatar horsemen or North African corsairs. A raiding party would
typically descend on an isolated village and carry away its inhabitants—or
rather those who were commercially useful, particularly young women and young
boys.

There was a time farther back, however, when
Europeans were accomplices in this trade and when it provided most of their
foreign exchange. This was during the Dark Ages and the early Middle Ages,
specifically the 8th to 12th centuries.

The slave trade was a godsend for the elites of
France, Germany, and Italy. With the collapse of the Western Roman Empire in the
5th century, they had to dip into their gold reserves to buy foreign luxury
goods from the Middle East, generally clothing, upholstery, tapestries,
carpets, and other precious fabrics (Skirda, 2010, pp. 56-57). By the 8th
century, these reserves had been almost completely exhausted. Gold was giving
way to silver, and even that medium of exchange was being debased. Western
Europe had largely reverted to an economy of autarky, its shrunken towns and
cities no longer major centers of trade. Most people produced everything they
needed within their local village or manor.

Would Western Europe have eventually returned on its
own to an international trading economy? Perhaps, although revival of trade
would have become more difficult once the elites had become accustomed to
autarky. As things turned out, they found the means to buy foreign luxury goods
almost at the same time their gold reserves ran out. The 8th century brought
the rapid expansion of a new civilization, Islam, into the Middle East, North
Africa, and Spain. Its Arab elite was darker-skinned than the Greco-Roman or Visigothic elites it displaced. It was also more polygynous. A new market had
come into being, a market for wives and concubines. European women were
especially sought after, not because they were exotic but because their fair
skin and fine facial features corresponded to notions of beauty that were
indigenous to Arab culture (see previous post).

And so began the commodification of European women.
Initially, this trade involved prisoners of war captured during the Islamic
wars of expansion. Soon, however, a peaceful trading relationship developed. It
was officially prohibited by Christian emperors and popes alike, but “in
reality, people closed their eyes and everything was tolerated in exchange for
good gold dinars” (Skirda, 2010, p. 75).

The women came from a belt of territory stretching
from the Elbe in the West to the Volga in the East. This territory was
inhabited by Slavic tribes—the ancestors of today’s Poles, Czechs, Slovaks,
Byelorussians, Ukrainians, and Russians. They were typically prisoners of war
who had been taken during fighting either between Germans and Slavs or among
different Slavic tribes:

Only the adolescent boys and girls—the
Slavonici—were spared, enslaved, and immediately sold to the merchants
accompanying the armies. The Barbarian-ruled West, abandoned by major
international trade and bereft of gold, was able to get gold by trading in
slaves, who were almost exclusively Slavs. These objects of servile trade and
commerce would be integrated into harems and used as military slaves or
eunuchs. Adults and children were eliminated for obvious reasons. They did not
correspond to the Muslim demand for young virgin girls and beardless boys and
it was out of the question to gather children and raise them. The traders had
neither the time nor the willingness and more importantly it would not have
been cost-effective. Later, they would spare the lives of more captives, by
selecting them according to their capacities for productive work and by using
them to the limit of their strength at laborious physical tasks (Skirda, 2010,
pp. 85-86).

The captives were taken overland by various routes:
through Germany and France to Muslim Spain; through Venice and by ship to the
Middle East; or down the Dniepr, the Don, or the Volga to the Middle East via
the Black Sea or the Caspian. How many were traded? It’s difficult to say, but
Skirda (2010, p. 6) advances a figure between several tens of thousands and
several hundreds of thousands for the period extending from the 8th to 12th
centuries.

It was this trade, more than any other, that revived
the old trading networks not only between Europe and the Middle East, but also
within Europe itself. The balance of foreign exchange also shifted in Europe’s
favor, thus giving the elites of France, Germany, and Italy the means to buy not
only foreign goods but also local products, thereby stimulating a long economic
recovery that would take Europe out of the Dark Ages. As Skirda notes
ironically:

The Italians who […] were the
“great initiators of Europe” […] became the promoters of trading companies,
creators of credit, restorers of currency. The only major oversight [of
historians]: all of that was accomplished through the trade in Slavs. It is
easier to understand why almost all historians and commentators have silently
observed this phenomenon. It is difficult for them to acknowledge that the
economic renaissance of the West of the 10th and 11th centuries was achieved
through human trafficking! (Skirda, 2010, p. 112)

Saturday, September 7, 2013

Why do humans have so little body hair? This
question is addressed by Sandel (2013) in his comparative review of hair
density in 23 primates and 29 nonprimate mammals. There seems to have been a
long-term trend towards hairlessness in our primate ancestors:

[…] all primates, and chimpanzees
in particular, are relatively hairless compared to other mammals. This suggests
that there may have been selective pressures acting on the ancestor of humans
and chimpanzees that led to an initial reduction in hair density. (Sandel, 2013)

Across species, hair density negatively correlates
with body mass. This correlation may exist because bigger primates are of more
recent origin. Or hairlessness may be a way to disperse the excess heat generated
by a larger body, since the increase in surface area (and hence the ability to
dissipate heat) does not keep pace with the increase in mass. Sandel rejects
this ‘heat load’ hypothesis:

Wheeler (1984, 1985) hypothesized
that the low hair density in humans was associated with increased sweating
capabilities. If the low hair density among primates represents a
thermoregulatory adaptation, there should be a negative correlation between
eccrine sweat gland density and hair density. There are no comparative data on
eccrine sweat gland density in primates, but the distribution of eccrine sweat
glands (presence vs. absence in certain body regions) is not consistent with
the thermoregulatory predictions (Montagna, 1972; Grant and Hoff, 1975). In
sum, the negative relationship between hair density and body mass cannot
currently be explained. (Sandel, 2013)

He concludes that the evolutionary trend towards
hairlessness cannot be due to anything specifically human, such as bipedality.
Denudation of the skin must have begun even before the common ancestors of
humans and chimpanzees went their separate ways:

If chimpanzees are indeed
relatively hairless compared to other mammals, there may have been a selective
pressure acting on the ancestor of humans and chimpanzees that led to an
initial reduction in hair density. Current hypotheses for human hair evolution
focus on uniquely human traits, such as bipedality or longdistance running. If
a reduction in terminal hair density is shared with chimpanzees, we may need to
develop hypotheses for human “hairlessness” based on traits that are shared
among chimpanzees, bonobos, and humans. (Sandel, 2013).

Social
signaling?

One cause may have been a growing tendency among
primates to replace fur coloration with skin coloration as a means to provide
conspecifics with key information about oneself: age, sex, social rank,
availability for mating, etc. (Higham, 2009). Increasingly complex social
relations would have created more information to signal, thereby driving selection
for denudation of the body surface. Since social status can change over a short
span of time, skin might have edged out fur as a better way to convey this information
to others.

In ancestral humans, the key signaler seems to have been
the adult female, as Charles Darwin noted:

As woman has a less hairy body
than man, and as this character is common to all races, we may conclude that
our female semi-human progenitors were probably first partially divested of
hair; and that this occurred at an extremely remote period before the several
races had diverged from a common stock. As our female progenitors gradually
acquired this new character of nudity, they must have transmitted it in an
almost equal degree to their young offspring of both sexes; so that its
transmission, as in the case of many ornaments with mammals and birds, has, not
been limited either by age or sex. […]

The females of certain anthropoid
apes, as stated in a former chapter, are somewhat less hairy on the under
surface than are the males; and here we have what might have afforded a
commencement for the process of denudation. (Darwin, 1871, pp. 377-378)

If we consider women’s skin, particularly its visual
and tactile properties, it tends to be softer, smoother, paler, and more
pliable. These are also the properties of infant skin. In this and other ways (e.g.,
face shape, pitch of voice), the adult female body tends to mimic the infant
schema, perhaps as a way to trigger the same mental and behavioral responses. There
may thus have been a three-stage evolutionary process where human skin lost its
body hair through a selection pressure that first targeted infants and then
women, with men becoming denuded as a side effect.

Infant skin
color and social signaling

Primate infants use both skin and fur coloration to
indicate their age class:

The coat color of the newborn
infant of all species of Old World monkeys for which information is available
is different from that of an adult of the same species. Often this difference
is extremely striking, as in the dark-brown fur of the newborn langur. Skin
color of the infant langur, baboon, and macaque is pink, in contrast to the
almost black skin of the older infant or adult. The infant’s pink face, hands,
and feet and its large pink ears are in sharp contrast to its dark brown fur.
The natal coat color is present during the first two or three months of life,
when the infant most needs protection and nourishment from its mother and older
monkeys. It is almost certainly more than coincidence that the duration of coat
color difference coincides with a period of dependency, when it is essential
that the young be sheltered and protected by older animals (Jay, 1962)

The skin seems to have reached its current
denudation relatively late in hominid evolution, perhaps even after the fork
that led on the one hand to Neanderthals and on the other to modern
humans.Neanderthals survived subzero
climates without tailored clothing, and their sites yield only hide scrapers
that could have served only to make blankets or ponchos. Microwear analysis
shows that these scrapers were used for the initial phases of hide preparation,
but not for the more advanced phases of clothing production (Hoffecker, 2002,p. 107). In contrast, modern human sites abound in eyed bone needles and bone
awls (Hoffecker, 2002, pp. 107, 109, 135, 252). Further evidence for the
relative lateness of tailored clothing is the recent origin of the human body
louse, which lives in clothing and first appeared perhaps 83,000 to 170,000
years ago (Toups et al, 2011). Finally, Neanderthal infants seem to have clung
to their mothers’ fur: “Chimpanzees have ridges on their finger bones that stem
from the way that they clutch their mother’s fur as infants. Modern humans
don’t have these ridges, but Neanderthals do” (Cochran and Harpending, 2009).

Denudation would have made the pale pink skin of
infants visually more important. This pallor is striking in darker-skinned
humans and seems to be appreciated by parents. A life story of a !Kung woman
records why she would not kill her newborn child: “Uhn, Uhn … I don't want to
kill her. This little girl is too beautiful. See how lovely and fair her skin
is?” (Shostak, 2000, p. 70). In Kenya, newborn infants are often called mzungu ('European' in Swahili), and a
new mother may tell her neighbors to come and see her mzungu (Walentowitz, 2008). Among the Tuareg, children are said to
be born "white" because of the freshness and moisture of the womb
(Walentowitz, 2008). The cause is often thought to be a previous spiritual
life:

There is a rather widespread
concept in Black Africa, according to which human beings, before
"coming" into this world, dwell in heaven, where they are white. For,
heaven itself is white and all the beings dwelling there are also white.
Therefore the whiter a child is at birth, the more splendid it is. In other
words, at that particular moment in a person's life, special importance is
attached to the whiteness of his colour, which is endowed with exceptional
qualities. (Zahan, 1974, p. 385)

Another Africanist makes the same point: "black
is thus the color of maturity [...] White on the other hand is a sign of the
before-life and the after-life: the African newborn is light-skinned and the
color of mourning is white kaolin" (Maertens, 1978, p. 41).

Conclusion

Loss of body hair was a long-term evolutionary trend
in ancestral hominids and even ancestral primates, being perhaps a response to a
greater need for social signaling. In ancestral humans, the selection pressure
seems to have gone through three stages, initially targeting infants and only
later women and then men.

Among nonhuman primates, the relatively depigmented
skin of infants has long exercised the signaling function of calming aggressive
impulses in parents and stimulating protective, nurturing behavior. Women seem
to have mimicked infant skin for the same purpose, perhaps because of the longer
period of infant dependency and their correspondingly greater vulnerability
during this period.

References

Alley, T.R. (1980). Infantile colouration as an
elicitor of caretaking behaviour in Old World primates, Primates, 21, 416-429.

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Welcome to my blog! For the most part, this page will be an extension of my website, with comments relating to my research. But it will also branch out into more general discussions of human evolution.